How to make 2 objects not intersect each other?
If you're trying to animate a character that is to behave as normal, I don't think you want to try to use physics to solve problems with floor interaction. I personally don't know such an approach to be a recommended workflow in any 3D package. Floor collision difficulties are just something you are going to have to learn to deal with. One way to do it is by taking care when animating. If you simply ensure that all your foot keyframes are in the right position, and set in the correct order, no drifting through the floor plane will ever happen. For example, if you set the extreme forward and extreme back positions for an IK foot in a walk cycle, and do this before setting any other keyframes, then the foot has no choice but to slide straight back and forth between these two positions, and could be counted on to perform absolutely no movement along the vertical axis. Such an approach can be an essential foundation for all the keyframes which follow, as these two will ensure that no movement below the floor plane takes place.
Alternatively, you can use location constraints to help ensure that undesired behaviors never become possible, instead of relying on keyframes alone. But even here, care will have to be taken, particularly while setting up the character itself, so as to ensure that the bone positions of the armature properly meet with the floor plane at the same time that the character's foot geometry meets it.
Physics is a resource intensive operation. It is slow, prone to bugs, and not at all ideal for the purpose of general character rigging, in my opinion. It's certainly not a one-button alternative to planning your rig.